The younger David said his father's bucket list has long included "tracking gorillas," so instead of planning a big 60 th birthday bash, the family took what Brandon David described as an epic adventure.

They started out by visiting London, and then traveled for five days through Uganda. That's where his father had an unforgettable encounter with a gorilla.

During their travels through Uganda, the Davids - Brandon is from San Francisco and his father from Newport Beach, Calif. - visited Bwindi Impenetrable National Park, a rainforest animal sanctuary that is home to a number of wildlife species, including an estimated 320 mountain gorillas.

Mountain gorillas are considered critically endangered. There are fewer than 900 of them remaining in the world today, and they live in four national parks located in three African nations, according to the African Wildlife Federation.

Answering emailed questions from France, the next leg of the family's journey, Brandon David described getting to the Ugandan sanctuary. They drove for nearly three hours to reach the entrance of the forest, and then hiked inside for more than two hours. The vegetation there was so dense that their guide used her machete to hack them a path, he wrote to ABCNews.com.

The found a family of 12 gorillas and spent more than an hour observing them.

Then, his father sat down to rest, and a black gorilla climbed down a tree and sat a short distance across from him. Brandon David started shooting on his cellphone, and his stepmother, Heather, was shooting on her camcorder.

On the video, you can see the gorilla close the gap, getting right up to the elder David, who did not make even the smallest movement.

"Initially my dad did not look him in the eye, but our guide said it was O.K. to look at him. They locked eyes, and then the gorilla decided to get a closer look. My dad swears he was not afraid, but the rest of us sure were," Brandon David wrote.

"The gorilla breathed hot air into my dad's ear for a few seconds, then pressed his lips against his cheek. The guide gave a low gutteral gorilla noise and the gorilla scampered off. We all commented on how surreal the experience was, and we certainly will never forget it."

He added that as the family hiked out of the valley, the gorilla family followed "and played around as we sat and ate our lunch (bananas)," he added. "It took another two hours to hike out of the jungle. It was a truly wild experience."